Remove tag system, use versions only for artifact references

Tags were mutable aliases that caused confusion alongside the immutable
version system. This removes tags entirely, keeping only PackageVersion
for artifact references.

Changes:
- Remove tags and tag_history tables (migration 012)
- Remove Tag model, TagRepository, and 6 tag API endpoints
- Update cache system to create versions instead of tags
- Update frontend to display versions instead of tags
- Remove tag-related schemas and types
- Update artifact cleanup service for version-based ref_count

frontend/src/components/DependencyGraph.tsx

@@ -170,7 +170,7 @@ function DependencyGraph({ projectName, packageName, tagName, onClose }: Depende
           label: `${artifact.project}/${artifact.package}`,
           project: artifact.project,
           package: artifact.package,
-          version: artifact.version || artifact.tag,
+          version: artifact.version,
           size: artifact.size,
           isRoot,
           onNavigate,

frontend/src/components/DragDropUpload.test.tsx

@@ -524,7 +524,7 @@ describe('DragDropUpload', () => {
       }
       vi.stubGlobal('XMLHttpRequest', MockXHR);
       
-      render(<DragDropUpload {...defaultProps} tag="v1.0.0" />);
+      render(<DragDropUpload {...defaultProps} />);
       
       const input = document.querySelector('input[type="file"]') as HTMLInputElement;
       const file = createMockFile('test.txt', 100, 'text/plain');

frontend/src/components/DragDropUpload.tsx

@@ -13,7 +13,6 @@ interface StoredUploadState {
   completedParts: number[];
   project: string;
   package: string;
-  tag?: string;
   createdAt: number;
 }
 
@@ -87,7 +86,6 @@ export interface DragDropUploadProps {
   maxFileSize?: number; // in bytes
   maxConcurrentUploads?: number;
   maxRetries?: number;
-  tag?: string;
   className?: string;
   disabled?: boolean;
   disabledReason?: string;
@@ -230,7 +228,6 @@ export function DragDropUpload({
   maxFileSize,
   maxConcurrentUploads = 3,
   maxRetries = 3,
-  tag,
   className = '',
   disabled = false,
   disabledReason,
@@ -368,7 +365,6 @@ export function DragDropUpload({
             expected_hash: fileHash,
             filename: item.file.name,
             size: item.file.size,
-            tag: tag || undefined,
           }),
         }
       );
@@ -392,7 +388,6 @@ export function DragDropUpload({
         completedParts: [],
         project: projectName,
         package: packageName,
-        tag: tag || undefined,
         createdAt: Date.now(),
       });
 
@@ -438,7 +433,6 @@ export function DragDropUpload({
         completedParts,
         project: projectName,
         package: packageName,
-        tag: tag || undefined,
         createdAt: Date.now(),
       });
 
@@ -459,7 +453,7 @@ export function DragDropUpload({
       {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
-        body: JSON.stringify({ tag: tag || undefined }),
+        body: JSON.stringify({}),
       }
     );
 
@@ -475,18 +469,15 @@ export function DragDropUpload({
       size: completeData.size,
       deduplicated: false,
     };
-  }, [projectName, packageName, tag, isOnline]);
+  }, [projectName, packageName, isOnline]);
 
   const uploadFileSimple = useCallback((item: UploadItem): Promise<UploadResult> => {
     return new Promise((resolve, reject) => {
       const xhr = new XMLHttpRequest();
       xhrMapRef.current.set(item.id, xhr);
-      
+
       const formData = new FormData();
       formData.append('file', item.file);
-      if (tag) {
-        formData.append('tag', tag);
-      }
 
       let lastLoaded = 0;
       let lastTime = Date.now();
@@ -549,13 +540,13 @@ export function DragDropUpload({
       xhr.timeout = 300000;
       xhr.send(formData);
 
-      setUploadQueue(prev => prev.map(u => 
-        u.id === item.id 
+      setUploadQueue(prev => prev.map(u =>
+        u.id === item.id
           ? { ...u, status: 'uploading' as UploadStatus, startTime: Date.now() }
           : u
       ));
     });
-  }, [projectName, packageName, tag]);
+  }, [projectName, packageName]);
 
   const uploadFile = useCallback((item: UploadItem): Promise<UploadResult> => {
     if (item.file.size >= CHUNKED_UPLOAD_THRESHOLD) {

frontend/src/components/GlobalSearch.tsx

@@ -233,7 +233,7 @@ export function GlobalSearch() {
                     const flatIndex = results.projects.length + results.packages.length + index;
                     return (
                       <button
-                        key={artifact.tag_id}
+                        key={artifact.artifact_id}
                         className={`global-search__result ${selectedIndex === flatIndex ? 'selected' : ''}`}
                         onClick={() => navigateToResult({ type: 'artifact', item: artifact })}
                         onMouseEnter={() => setSelectedIndex(flatIndex)}
@@ -243,7 +243,7 @@ export function GlobalSearch() {
                           <line x1="7" y1="7" x2="7.01" y2="7" />
                         </svg>
                         <div className="global-search__result-content">
-                          <span className="global-search__result-name">{artifact.tag_name}</span>
+                          <span className="global-search__result-name">{artifact.version}</span>
                           <span className="global-search__result-path">
                             {artifact.project_name} / {artifact.package_name}
                           </span>